The invention relates to a method for synchronizing a radio communication system divided into radio cells a base station, a mobile station and a radio communication system.
Cellular radio communication systems, in particular mobile radio systems, are subdivided into synchronized and unsynchronized radio communication systems.
In the case of the former, base stations of adjacent radio cells are synchronized with each other in respect of time and/or carrier frequency. For the purposes of synchronization, in particular for time synchronization, GPS receivers are for example deployed at the base stations or base stations are synchronized by synchronization signals that are complex to exchange. The transmission of synchronization signals also takes up radio transmission resources, which are then no longer available for chargeable user data transmissions (payload).
In the case of unsynchronized radio communication systems, base stations of adjacent cells are not synchronized with each other.
Synchronization methods are particularly important in mobile radio networks in particular, when so-called Orthogonal Frequency Division Multiplexing or OFDM transmission methods are used. Services requiring high data speeds, for example video transmissions, can be transmitted in a cost-effective manner by OFDM data transmissions. OFDM data transmission takes place by so-called subcarriers, which are formed by subdividing an available bandwidth. As these subcarriers are particularly advantageously used in a multiple manner in adjacent cells, resulting co-channel interference should be taken into account during planning and operation.
So that radio transmission resources can be allocated or managed (Radio Resource Management RRM) in an optimum manner in respect of data transmission, frequency and/or time synchronization must be precise, depending on the radio transmission methods used in each instance. The two synchronization methods mentioned by way of example, because they are based on received mobile station signals, are largely dependent both on the quality and number of received mobile station signals, as far as precision is concerned.